POTATO DISEASES

Excessively rapid potatoes tubers growth, especially during favourable water and soil fertility conditions, causes internal cavities and hollow heart. Rots seldom follow although market quality is reduced.

Knobbiness and irregular shape—second growth is results when tubers resume growth because of improved environmental conditions after the tuber’s initial expansion under less favourable conditions.
One example is water following drought. Tissue around the apex may resume growth, causing an enlarged end.

Lateral eyes enlarge to produce knobs.
Heat sprouts occur when sprouts develop from potatoes tubers that have suffered from high temperatures and grow either as a sprout or a leafy aboveground stem.

Tuber chaining occurs when a series of secondary tubers develop on a single stolon.
Resumption of potatoes tuber growth following quiescence is often accompanied by carbohydrate translocation from the basal part to another part of the same tuber, leaving a wet, soft mass, jelly end rot.

Also, carbohydrates may move from one tuber to a different tuber more terminally situated on the same stolon. When this or jelly end rot occurs, market quality is greatly reduced.
Some varieties are more prone to injury than others.
More space between plants help avoid excessively large potatoes tubers and to promote uniform stands.

Regulate water supply to provide uniform growing conditions.

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Potatoes grow best in soils of pH 5.0 to 7.0. Deficiencies or toxicities of major or minor elements may be caused by excessive solubility or fixation in the soil through interaction with soil colloids or chemicals.

Nitrogen (N) requirements increase rapidly with potatoes plants growth.
When N is translocated to upper leaves excessively from the lower leaves, they then become yellow.

Later, if the deficiency is not corrected by fertilization, the entire potato plant becomes yellow and fails to grow properly.

Severity of plant response depends on the level of N deficiency. N toxicity from ammonium or nitrites may follow degradation of nitrogencontaining fertilizers in certain soil conditions.

Phosphorus (P) deficiency follows P fixation in a wide range of soil types.

Symptoms include retardation in growth of terminals; small, spindly, somewhat rigid plants with crinkled or cup-shaped leaves; darker than normal colour; possibly a delay in maturity; and reduced yield.

Potatoes tubers may have internal rusty brown necrotic flecks similar to internal heat necrosis.
Because P is frequently fixed in the soil, fertilizer banding applications lateral to the seed piece are superior to broadcasting.
Potassium (K) deficiency is common in light, easily leached soils.

Early symptoms are dark or bluish green glossy foliage.
Later, older leaves of potatoes plants become bronzed and necrotic (superficially resembling early blight), and senesce early.
Necrotic, somewhat sunken corky lesions form on the tuber surface, particularly at the stolon attachment.
Potatoes tubers are predisposed to black spot, and when cooked tend to darken.

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(Aster Yellows, Stolbur, Haywire) These diseases, caused by mycoplasma-like organisms that resemble bacteria that lack a cell wall and are thus of indefinite shape, can severely affect yield and tuber sprouting and quality. They are transmitted by leafhoppers.

Symptoms of Purple Top Wilt
Symptoms of Purple Top Wilt include development of shoots and/or aerial tubers in leaf axils.
Potatoes plants become stunted and apical leaves may curl and turn yellowish or purplish. Plants may wilt.
Potatoes tubers from infected plants do not sprout normally.

They are often small, flaccid, malformed, and without sprouts or with thin “hair sprouts”.
Witches’-broom is a symptom caused by another strain of mycoplasma.

Although these diseases are usually of minor importance in potato, being current-season problems only, hundreds of species of vegetable, ornamental, and field crop plants and weeds are susceptible to them.

Management

Leafhoppers cannot acquire the pathogen from potato, and they can be partly controlled by killing weed hosts from which these vectors move to the potato crop.

Leafhoppers can often be avoided by planting later in the growing season after their migration has ended.
The principal leafhopper vectors develop on convolvulaceous weeds, grasses, and small grains.

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